Crop harvesting machine with variable header float

ABSTRACT

In a crop harvesting machine there is provided a pair of hydraulic float cylinders or springs for a header such as a rotary mower relative to a self-propelled vehicle, where a float spring force is controlled to provide a predetermined lifting force is provided to the header. The spring force is varied in response to detection of ground speed to decrease the lifting force at higher ground speeds. A position sensor is used to generate an indication of movement and/or acceleration. The electronic control is arranged, in response to changes in the sensor signal, to temporarily change the control signal to vary the lifting force and thus change the dynamic response of the hydraulic float cylinder. In order to reduce static friction so that the system can react quickly, an arrangement is provided for causing relative reciprocating movement in an alternating wave pattern between the piston and cylinder.

This invention relates to crop harvesting machine with a variable headerfloat weight.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a cropharvesting machine comprising:

a self-propelled support vehicle for running over ground carrying a cropto be harvested;

a crop cutting header including at least one ground engaging componentfor providing a supporting force from the ground;

a support apparatus providing a lifting force for supporting the headerfrom the vehicle for upward and downward floating movement of theheader;

a control system arranged to provide a value of said lifting force sothat a predetermined proportion of a supporting force is supplied by thesupport apparatus and a remaining portion is supplied by said at leastone ground engaging component in engagement with the ground;

said control system being arranged in response to a ground speed signalto temporarily change the lifting force.

Preferably the crop cutting header comprises a rotary mower having aplurality of transversely spaced cutting disks. The variability of theheader float based on ground speed is particularly applicable to thehigher ground speeds of 5 to 15 mph obtainable with rotary mowers.

Preferably the control system is arranged such that the lifting force isreduced to increase the weight of the header on the ground when theground speed is higher.

Preferably the control system is arranged such that the lifting force isreduced to increase the weight of the header on the ground when theground speed is greater than 5 mph.

In one arrangement the control system is arranged such that the liftingforce is reduced to increase the weight of the header on the groundproportional to ground speed. That is for example the lifting force maybe directly proportional to ground speed. However other algorithms canbe used to increase the weight such that the lifting force is reduced toincrease the weight of the header on the ground in response to analgorithm dependent on ground speed.

Preferably there is provided a ground speed sensor for providing aninput to the control system.

Preferably the control system is arranged subsequently in response toreducing the lifting force to revert to a set value.

Preferably the control system is arranged to temporarily vary thelifting force in response to detected movement of the header relative tothe vehicle.

Preferably the control system is arranged to temporarily vary thelifting force in response to detected acceleration of the headerrelative to the vehicle.

Preferably the electronic control system is arranged upon detection ofan end of said acceleration to vary the lifting force.

Preferably there is provided a position sensor for generating a positionsignal indicative of a position of the header in said movement and thecontrol system is arranged to calculate from the position signal avelocity and acceleration of the header.

Preferably the control system is arranged to provide a plurality ofpreset flotation weights for different ground speeds.

In one preferred arrangement as describe hereinafter, the supportapparatus comprises a mechanical spring and the control system isarranged to vary a spring force of the mechanical spring.

In another arrangement, the support apparatus including at least onehydraulic float cylinder arranged such that application of a hydraulicfluid under hydraulic pressure to said at least one float cylindercauses a lifting force to be applied to the crop engaging assembly bymovement of said at least one float cylinder which lifting force isproportional to said hydraulic pressure.

In this arrangement there is provided a source of hydraulic fluid forsupply of the hydraulic fluid to said at least one float cylinder at apressure greater than said hydraulic pressure and a return for thehydraulic fluid.

A valve arrangement is provided for controlling a flow of and pressureof said hydraulic fluid from said source to said at least one floatcylinder, the valve arrangement being connected to said at least onefloat cylinder such flow of fluid into and out of said at least onefloat cylinder is controlled by the valve arrangement at said hydraulicpressure controlled by the valve arrangement and including an electroniccontrol system for supplying a control signal to the valve arrangementto change said predetermined pressure in dependence on a value of thesignal.

The valve arrangement comprises a first connection to said source, asecond connection to said at least one float cylinder, a thirdconnection for discharge of said hydraulic fluid to said return and avalve operating system operable to control flow of hydraulic fluid fromsaid source to said at least one float cylinder and flow of hydraulicfluid from said at least one float cylinder to said return so as tomaintain said hydraulic pressure in said at least one float cylinder ata predetermined pressure set in dependence upon said control signal fromsaid control system.

A sensor is arranged to provide a sensor signal to said electroniccontrol system in response to movement of the crop engaging assembly insaid upward and downward floating movement of the crop engagingassembly, the electronic control system is arranged to provide a setvalue of said control signal to provide said lifting force at a setvalue to maintain said predetermined proportion of said supporting forceand the electronic control system is arranged in response to said sensorsignal to temporarily change the control signal to temporarily changethe lifting force.

Preferably the electronic control system is arranged subsequent to thetemporary change, in response to said sensor signal, to revert to theset value. In this way, preferably, the electronic control system isarranged in response to changes in said sensor signal to temporarilychange the control signal to vary the lifting force and thus change theresponse of the hydraulic float cylinder in response to detectedmovement of the crop harvesting component.

For example the electronic control system is arranged upon detection ofan end of the acceleration in said upward floating movement to changethe control signal to decrease the lifting force to dampen the upwardmovement.

In this way the control system can be used to increase the lifting forcedynamically during the time that the header is being lifted by contactwith the ground or another obstacle so as to improve the response toforces from ground contact. In addition as soon as the ground contact isremoved thus halting any further acceleration, the lifting force can besignificantly reduced so that the weight of the header is re-applied inthe downward direction thus damping any further upward floatingmovement. This avoids or reduces the situation where the header islifted by ground force or engagement with an obstacle and then remainslifted for an extended period of time thus interfering with the cuttingof the crop while the header remains raised.

It will be appreciated that the dynamic control of the lifting forcesdepending upon the movement of the header can be used both in a groundflotation mode and also when cutting at a set raised height. In thelatter condition, float action is typically provided in order to floatthe header over any obstacles, even though the main cutting action is atthe raised position from the ground. Also in some cases such as ditchesand mounds the ground height may vary sufficiently that the headerengages the ground even though nominally set at a height above theground. In all of these cases, therefore, the dynamic control of thelifting forces increases the available force to lift the header over thechange in height of the ground or over the obstacle. At the same timethe lifting action is halted or reduced when the obstacle is cleared soas to reduce the time that the header remains elevated above therequired condition.

In a situation where the header is at a raised cutting height, thedownward forces can also be dynamically controlled to most effectivelyreturn the header to the required cutting height. Thus the downwardforces may be increased at the beginning of the downward movement andmay be reduced toward the end of the downward movement to bring theheader more smoothly back to its required height.

In order to provide the best damping force, preferably the electroniccontrol system is arranged to change the control signal to decrease thelifting force to a value less than said set value. The header willtherefore accelerate downwardly in view of this reduced lifting forceuntil the header reaches the ground whereupon the downward accelerationis halted and the control system reapplies the set value.

In a symmetrical manner, preferably the electronic control system isarranged upon detection of acceleration in the downward floatingmovement to change the control signal to decrease the lifting force toassist the acceleration in said downward floating movement. That is,when the header has been riding on the ground with no float required,and when a dip in the ground requires that the header fall to the lowerground level, the lifting force can be rapidly decreased so as to assistthe downward movement of the header using the weight from the header.Also the electronic control system can be arranged upon detection of anend of said acceleration in said downward floating movement, that is theheader has re-engaged with the ground, to change the control signal toincrease the lifting force to dampen said downward movement.

Preferably the sensor comprises a position sensor for generating aposition signal indicative of a position of the cylinder in its movementand the electronic control system is arranged to calculate from theposition signal a velocity and acceleration of the crop harvestingcomponent. However other sensor arrangements may be provided includingfor example a specific acceleration detection device and a specificrelative movement detection device, all of which senses are now readilyavailable in effective and inexpensive form due to their wide usage inother areas.

Preferably the electronic control system is therefore arranged toachieve a comprehensively adjustable spring rate for the dynamics of theflotation system.

Preferably the electronic control system is therefore arranged toachieve comprehensively adjustable damping for the dynamics of theflotation system.

In this invention, the electronic control system can be arranged toachieve comprehensively adjustable flotation system dynamics based onoperating state of the implement including but not limited to implementheight, ground speed and changes in terrain (incline angle, etc)

in additional preferably the electronic control system can be arrangedto allow for the operator to select from preset flotation systemdynamics which can be tailored to different field conditions andimplements.

In order to take advantage of the benefits of a hydraulic flotationsystem, the arrangement herein provides a system that reduces the effectof the friction in the flotation system to provide excellent groundfollowing capabilities. This system may be applied to windrowers andcombine adapters or any other agricultural implement that is floatingsuspended from carrier (hay tools, rakes, pickups, etc). The system canbe used when floating a header that is cutting on the ground as well asa header that is cutting at a height above ground level. While thesystem is particularly applicable to the main header float at the frontof the tractor, the same construction can also be used for the wingfloat on a flex draper header of the type shown in U.S. Pat. No.5,005,343 (Patterson) issued 9 Apr. 1991, the disclosure of which isincorporated herein by reference.

The system herein comprises one or more float cylinders that are used tosuspend the header from the carrier. At (or near) each cylinder is anelectronically controlled proportional pressure reducing relieving(PPRR) valve that controls the pressure at that cylinder. The valve iscontrolled by an electronic controller that takes pressure (or force)and position/velocity/acceleration feedback from the float system andvaries the pressure in the cylinder to obtain prescribed floatcharacteristics. A hydraulic pressure and flow is supplied to the valvefrom a source, that could be an accumulator charged to more than themaximum pressure demanded by the float system, a drive circuit that hasa minimum pressure that is more than the maximum pressure demanded bythe float system, or some other hydraulic source. However the pressurefrom the valve is applied directly and immediately to the cylinderwithout the presence of an accumulator in the circuit which wouldotherwise dampen the action of the pressure on the cylinder.

That is while most systems have an accumulator hydraulically connecteddirectly to the cylinder in float mode, the present arrangement uses anelectronically controlled PPRR valve directly between the pressuresource and the float cylinder. This allows the system to have veryprecise, instantaneous control of the float cylinder pressure so that itcan adjust the pressure based on instantaneous changes of the floatsystem. The accumulator systems are far less precise/responsive since achange of hydraulic pressure, when commanded, is split between cylindermovement and accumulator charge).

Each float cylinder has a respective position sensor, pressure sensorand pressure reducing relieving valve. The valve is then coupled to apressure source. The controller receives input from the sensors andcontrols each PPRR valve independently based on these input signals. Thesignal from the position sensor may be directly linked to the cylinderor may be linked to some other float link(s) that indicate headerposition. This signal can be used to calculate in the electronic controlsystem velocity and acceleration of the header as well as headerposition in the float range. The PPRR valves directly control thecylinders with no accumulator between the valve and the cylinder. Thisis the simplest representation of the system.

In another improvement of the invention that adds an accumulator,pressure sensor and control valve to enhance the response of the floatsystem. The controller receives an input signal from the pressure sensorand controls the valve to maintain a pressure range in the accumulatorthat is some value higher (200-250 psi for example) than the maximumpressure demanded at pressure sensors. This maximum pressure isdependent on header weight and can be determined via calibration usingconventional methods where the lifting force is increased graduallyuntil the header just lifts from the ground and by adding apredetermined value to that detected value, or by stored values based onheader ID for each header size and type.

With this method, the accumulator can supply instantaneous flow to thePRR valves likely more quickly than the load sense pump can respond tothe demand of flow.

Note that this type of float system may also be used to float the wingson a flex header. Using a cylinder to react the weight of the wing nearthe wing pivot and controlling that cylinder with the proposed system.

In addition to the above, the electronic control algorithms include amethod of controlling the output to the proportional PRR valvecontrolling the cylinder pressure, to encourage the header to follow theground more effectively.

Part of the electronic control that we use involves applying anoscillating control signal to the PPRR valve that supplies floatpressure to the cylinder. This creates a varying pressure in thecylinder that causes the cylinder to oscillate slightly. In doing so,the cylinder is always in motion and this reduces the friction effect ofthe cylinder seals. This oscillation of the pressure also helps tocompensate for the hysteresis or dead band of the proportional pressurereducing/relieving valve. This type of valve includes a spooloscillating back and forth between input and output fluid positions tomaintain the pressure at a position determined by the signal to thesolenoid of the valve where the position of the spool is controlled by apilot connection to the output pressure line. Typically the pilotconnection is internal to the valve itself and does not require a ductto the output line or to the controlled cylinder. This type of valve hasa dead band between where it relieves pressure and where it reducespressure.

A further feature of the system is that the system provides aprogrammable spring rate or float decay that can be customized to avariety of float requirements such as cutting height, ground speed, soilconditions etc. This spring rate can instantaneously and continually beadjusted based on sensor inputs from the float system, operator or othersystems such as radar, sonar or laser detection of obstacles and groundcontours.

A further feature of the system includes the ability to have adjustabledampening of the float system, again based on float requirements orsituations.

Another feature involves the increase or decrease of float cylinderpressure based on float position and direction of movement. For example,this allows us to decrease the float pressure if the header is detectedto be moving down (while cutting through a ditch for example) so thatthe header will follow the ground as the ground drops away. A similaradjustment can be made to increase the float pressure if the header isdetected to be moving up over a mound.

Another feature involves the increase or decrease of float cylinderpressure based on header velocity and/or acceleration.

Other features of the invention provide:

—a—Oscillating float pressure to reduce effects of proportional PRRvalve hysteresis as well as system (mechanical) and cylinder sealfriction.

—b—Sensing change in float position/last travel direction/velocity (thiscan be done with sensors measuring cylinder length, float link positionetc) and then decreasing/increasing float pressure to make the headerfall faster or raise faster.

—c—Different float characteristic settings based on ground condition,ground speed, crop, cutting on/off the ground.

—d—Programmed spring rate.

Feedback from a pressure sensor may not necessarily be required as thesystem may be able to just use the output to the PWM valve. For example,the valve output pressure can be correlated to valve electronic input sotechnically, if we send the valve a known signal, we can know whatoutput pressure the valve is set to. However typically the pressuresensor may be required due to changes in valve characteristics due totemperature changes, wear, vibration etc which may be too large to makethis viable.

The signal from the pressure sensor can be used as a feed back toconfirm that the valve is indeed outputting the required output pressureas set by the control signal. Thus it may be possible to provide anarrangement in which the feedback is used only periodically to check theoutput value so that the signal from the pressure sensor is not directlyand repeatedly used by the control system. That is, periodically theoutput pressure can be checked and a correction factor used insubsequent calculations by the control system, if it is found that themeasured output pressure does not match the intended value as set by thecontrol device.

As an alternative, an arrangement can be made to work where the systemknows the position of the header in the float range (from the positionsensors) and can use this knowledge to make changes to the floatpressure to find an optimum value that places the header with a minimalground force based on velocity and acceleration calculations.

While the alternating wave movement is preferably provided by a waveform in the signal from the control device, it also possible to use analternative method in which a mechanical version of dithering such as apiston/crank arrangement that oscillates the float pressure. For examplein a sickle cutter the system could use the pulsing of the knife drivecircuit as well.

Various methods of obtaining float supply pressure can be used includingdrive circuit pressure, drive circuit pressure with an accumulator andcheck valves, closed loop load sense pump.

Calibration is typically carried out by the conventional method in whichthe system is operated to increase float pressure until header justleaves the ground and then use the system to increase/decrease floatpressure to get optimum ground contact pressure. Other calibrationmethods can of course be used, many of which are known to personsskilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described in conjunction withthe accompanying drawings in which:

FIG. 1 is a side view of a vehicle having a header and a headerflotation system in accordance with the present invention. In thisembodiment, the vehicle is a windrower.

FIG. 2 is a schematic illustration of a simple arrangement of thecontrol system according to the present invention for use in the headerof FIG. 1.

FIG. 3 is a schematic illustration of a second arrangement of thecontrol system according to the present invention for use in the headerof FIG. 1 which includes an accumulator as a part of the fluid source toensure sufficient and immediate fluid flow to satisfy the PPRR valves.

FIG. 4 is a schematic illustration of a third arrangement of the controlsystem according to the present invention for use in the header of FIG.1 arranged to capture energy of header floating.

FIG. 5 is a flowchart showing the operation of the system.

FIG. 6 is a cross-sectional view through a vehicle of the type shown inFIG. 1 where the header is a rotary mower including cutting disks andthe support apparatus carrying the header from the vehicle comprises afloat spring.

DETAILED DESCRIPTION

FIG. 1 shows the present invention utilized in connection with theself-propelled windrower 100, however, it will be appreciated that theprinciples of the present invention are not limited to a self-propelledwind rower, or to any specific type of harvesting machine having aheader. The figure shows windrower 100, which comprises a tractor 102and a header 104. The header 104 is pivotally attached to the front endof the frame or chassis 106 of windrower 100 such that it can move upand down with respect to chassis 106.

Such attachment of the header 104 to the frame 106 is achieved through apair of lower arms 108 (only the left one being shown, the right onebeing in the same position and in mirror configuration on the right sideof the vehicle) pivoted at one end to the frame 106 and at the other endto the header 104 as well as through a central upper link 110.

The link 110 may take the form of a single or double hydraulic cylinder112 whose extension and retraction is controlled by the operator toremotely control the angle of the sickle bar 114 on the lower front ofthe header 104.

A single lift/flotation cylinder 116 is shown interconnecting the lowerarm 108 to the frame 106. Cylinder 116 supports each side of the header,i.e., each side of the header is supported by its own lift/flotationcylinder 116. Again, only the left side lift/flotation cylinder 116 isshown. The right side lift/flotation cylinder 118 is identicallyconstructed, configured, and arranged as left side lift/flotationcylinder 116 and is interconnected in the identical manner to the headerand the frame but is configured in mirror image form to that of the leftside of the vehicle.

A position sensor 120 is coupled to and between frame 106 and bell crank122 and is configured to sense the position of the cylinder. This can bedone at the cylinder or at another location such as at the relativeposition of bell crank 122 with respect to frame 106. The positionsensor shown here is a potentiometer providing a signal which varieswhen the header moves up and down (has a vertical component oftranslation) with respect to frame 106. In this sense, the positionsensor is also a height sensor which detects the height of the headerfrom the tractor. The particular arrangement of position sensor 120 withrespect to frame 106 and with respect to bell crank 122 can be varieddepending on the space available, the type transducer desired, and theresolution of the sensor.

The arrangement therefore provides a crop machine, typically a cropharvesting machine, comprising the support vehicle 102 for running overground to be harvested and a crop component, typically a harvestingheader 104, including a crop engaging system 114 and at least one groundengaging component or skid plate 128 for providing a supporting forcefrom the ground. The support apparatus 110, 106, 116 and 108 acts tosupport the crop harvesting header from the vehicle for upward anddownward floating movement of the crop harvesting header so that a partof a supporting force is supplied by the support apparatus and a partsupplied by the ground engaging component 128.

In FIG. 6, the vehicle 102 includes front ground wheels 99 each of whichcarries an upstanding header support arm 98 which carries a rotaryheader 97. The rotary header is of a conventional construction includinga series of rotary disks 91 carried on a cutter bar 89. The header canfloat upwardly and downwardly on links 96 controlled by a float spring95. The effective spring force of the spring is varied by a cylinder 94which acts to pivot a link 93 to move one end 92 of the spring 95. Theother end 90 of the spring is connected to the header to apply a liftingforce to the header. The link 93 when actuated by the cylinder acts tochange either the length of the spring 95 or the mechanical advantage ofthe spring or both so as to vary the effective spring force applied bythe spring to change the lifting force on the header. As the liftingforce is reduced, the weight of the header on the ground typicallyapplied through the cutter bar 89 increases.

The support apparatus shown in FIG. 2 includes at least one andtypically two hydraulic float cylinders 116 and 117 arranged such thatapplication of a hydraulic fluid under hydraulic pressure to the floatcylinders 116 and 117 causes a lifting force to be applied to the cropharvesting header by movement of the float cylinder which lifting forceis proportional to the hydraulic pressure applied to the cylinder.

The float cylinders include cylinder seals 116A over which the pistoncomponent slides relative to the cylinder component of the floatcylinder. The circuit 10 applying pressure to the cylinders includes asource 12 of hydraulic fluid for supply of the hydraulic fluid to thefloat cylinder at a pressure greater than a required hydraulic pressure.The source 12 includes a pump 16 and a drain 14 providing a return forthe hydraulic fluid.

The circuit includes two separate sections for supplying fluid underpressure to the respective cylinders 116 and 117, including for each arespective valve arrangement 18, 20 for controlling a flow of andpressure of the hydraulic pressure from the source to the respectivecylinders.

As explained previously, the valves are of the PPRR type which include aspool 21 which can slide back and forth within the valve to connectinlet and outlet ports 22, 23 to the line 24 to the respective cylinder.The spool is driven by a solenoid 25 so as to position the solenoid at arequired location to generate a required pressure depending upon asignal to the solenoid provided by a controller 28 on a control line 29.The spool is also controlled by pilot pressure on line 30 and 31connected respectively to the inlet and outlet to the valve. Such valvesare commercially available from many different suppliers and are knownas proportional pressure reducing/relieving valves. These act tomaintain the pressure within the cylinder as it supplied along the line24 at a predetermined value set by the signal on the line 29 from thecontrol system by repeatedly supplying and discharging fluid relative tothe cylinder through the ports 22 and 23.

The control signal to the valves is the generated and controlled by andelectronic control system in order to change the predetermined pressurein the respective cylinder in dependence on a value of the appliedsignal.

Thus the valve arrangement includes a first connection 33 to the source12 and a second connection 34 to the return together with the outlet 24to the cylinder.

The valve component operates to control flow of hydraulic fluid from thesource to the float cylinder and flow of hydraulic fluid from the floatcylinder to the return so as to maintain the hydraulic pressure in thefloat cylinder at a predetermined pressure set in dependence upon thecontrol signal from the control system. The control system 28 includes asubcomponent 35 which acts to generate an alternating wave signal so asto provide an arrangement for causing relative reciprocating movement inan alternating wave pattern between the piston component of the floatcylinder and the cylinder component of the float cylinder so as tomaintain movement between the components at the cylinder seals 122 toreduce the effect of static friction.

That is the relative reciprocating movement is provided by thealternating wave pattern signal applied by the electronic control systemto the valve arrangement to change the predetermined pressure independence on a value of the alternating wave signal.

The subcomponent 35 is controlled by the control system 28 so that thealternating wave pattern is applied only when the cylinder is in floatmode and not when the cylinder is used in a lifting or lowering state.

The circuit further includes pressure sensors 40 and 41 which detect thepressure in the fluid supply lines to the cylinders to provide a signalwhich is communicated to the control system 28. As the valves arearranged to provide the pressure output in response to the controlsignal supplied, the measurement of the pressure output is nottheoretically required. However in view of temperature and other changeswhich may occur, it is desirable to check the output pressure to ensurethat it does not drift over time and the is maintained at the requiredpressure as determined by the control signal. The feedback checkprovided by the pressure sensors can be carried out periodically and isnot part of the control system operation to generate the output signals.

The position sensors 120 and 121 which detect the position of thecylinders provide a signal which is supplied back to the control system28. The system may run using only input from the position sensors sincethe control system 28 can calculate from changes in the signal from theposition sensors both the velocity and acceleration of the cylinder andtherefore of the header. A suitable algorithm to make such calculationsis of course well-known to persons skilled in this art. However inaddition to the position sensors or as an alternative thereto, thesystem may include an accelerometer 42 mounted on the header at one ormore suitable locations to provide an output indicative of relativemovement of the header and acceleration of the header.

The circuit can further include an operator input 45 which allows theoperator to input various parameters as necessary for controlling thecontrol system 28. The control system also includes input linesresponsive to various parameters of the operating header including forexample a ground speed indicator 46 and a crop condition indicator 47.These are shown only schematically as persons skilled in the art candetermine suitable input parameters. A further input line can beprovided from a prediction system 48 which can use ground height andcrop height sensors to detect in advance and the intended height of thecutting action. The signal can be used to predict obstacles or requiredchanges in cutting height so that the control system can generatesuitable signals to raise or lower the cylinders 116, 117 to a requiredposition.

The electronic control system is arranged to provide dynamic control ofthe lift force applied by the cylinders to the header. Thus, in responseto any movement of the header detected by the position sensors or byother accelerometer and relative movement type sensors, the controlsystem can change the pressure applied to the cylinders by the controlvalves so as to increase or decrease the lifting force from the presetfloat condition to change the movement of the header.

In this way, for example, upon detection of acceleration in the upwardfloating movement the control system can act to change the controlsignal to increase the lifting force to assist the acceleration in theupward floating movement.

Furthermore the electronic control system can act upon detection of anend of the upward acceleration in the upward floating movement to changethe control signal to decrease the lifting force to dampen the upwardmovement.

These two dynamic actions can be used for example on impacting anobstacle or on rapid rise in the ground level to rapidly accelerate theheader upwardly to clear the ground and then to halt the upward movementby a damping action to cause the header to float back downwardly asquickly as possible. To force the header downwardly more quickly, theelectronic control system can act to change the control signal todecrease the lifting force to a value less than the set float value.

Symmetrically, the electronic control system can act upon detection ofacceleration in the downward floating movement to change the controlsignal to decrease the lifting force to assist the acceleration in thedownward floating movement and upon detection of an end of theacceleration in the downward floating movement to change the controlsignal to increase the lifting force to dampen the downward movement.

In FIG. 3 is shown an arrangement in which there is provided onadditional accumulator 60 which has a pressure sensor 61 and a supplyvalve 62. This accumulator can be used to provide or to ensuresufficient fluid flow to the inlet of the valves 18 and 20 to meet therequirements for rapid flow of fluid into the cylinders if required. Inthis way, if the pressure source 16 which comprises a pump hasinsufficient flow rate at startup, the flow can be provided by theaccumulator.

In FIG. 4 is shown on optional hydraulic schematic to capture energy ofheader floating can also be used.

In this version of the invention, the cylinders 116 and 117 are invertedrelative to that shown in FIGS. 2 and 3. Also the pressure supplied tothe cylinders from the valves 18 and 20 is opposed by pressure from asupply 201 including an accumulator 200 at a constant pressure so thatlift force is generated by a difference in pressure from the valves 18and 20 relative to that of the supply 201. In other words, the liftingaction is provided by the pressure from the source 201 and this isopposed by the pressure supplied by the valves 18 and 20 to decrease thelifting force to a value determined by the valves 18, 20 under controlof the control system 28. In order therefore to increase the liftingforce, the pressure in the cylinders supplied by the valves 18, 20 isreduced, and vice versa.

That is there is an additional accumulator 200 that supplies floatenergy to the float cylinders that is above what is normally required tofloat the header. The PPRR valves 18, 20 are controlled to add downforce to the cylinders 116, 117 to make the header float down to theground. The control system for the PPRR valves is similar to thearrangement described above but with this system, the flow and/orpressure required to adjust the float are lower.

Also with this system, the system is capturing the energy from theheader floating down, into the accumulator 200 using an interveningshut-off valve 203. A pressure sensor 202 and control valve 204 are usedin conjunction with the controller 28 to control the pressure in thisaccumulator system.

As set forth above, this is maintained at a constant value, which can beset at different values depending on various operating parameters, andthe variations in the lifting force are applied by the valves 18, 20 onthe upper side of the piston to apply a variation in the pressureopposing the constant upward force on the lower side of the piston.

Thus the float cylinders can be used in either orientation, and areshown inverted in this embodiment. It can be appreciated that the floatcylinders could be used in a pull configuration rather than a pushconfiguration as well. In all FIGS. 2, 3 and 4, the header weight is inthe downward direction. That is the variations in the pressure suppliedby the valves can be used in a number of different orientations tochange the lift force generated by the cylinders.

The sensors to collect information about the dynamic state of theimplement can include a linear potentiometer which measures theextension of the hydraulic cylinder and a pressure transducer providingfeedback of the supplied pressure. In other interpretations, the forcetransmitted to the implement through the hydraulic cylinder could bemonitored with a force transducer or the height of the implement fromthe ground could be measured either directly or indirectly.

In addition, instead of calculating velocity and acceleration from theposition sensor, movement sensors and accelerometers can be used toprovide direct signals proportional to these values.

The arrangement could be used to achieve a comprehensively adjustablespring rate for the dynamics of the flotation system of the implement

The arrangement could be used to achieve comprehensively adjustabledamping for the dynamics of the flotation system of the implement

The arrangement could be used to achieve comprehensively adjustableflotation system dynamics based on operating state of the implementincluding but not limited to implement height, ground speed and changesin terrain (incline angle, etc)

The arrangement could allow for the operator to select from pre-setflotation system dynamics which can be tailored to different fieldconditions and implements.

While existing float systems can achieve acceptable ground forces whenthe header is stationary, because the applied force is generallyindependent of the header's state of motion, the header will stilldynamically respond based on its mass, not the set point of the floatsystem. For example, the float system could be set such that the groundforce is 500 lbs, however, in order for the header to accelerate upwardsor downwards, an additional input of force is required. Based onNewton's second law (F=ma), this additional force will generate anacceleration in the header which is inversely proportional to theheader's mass. Therefore, while the header may be statically light(i.e., light when it is stationary), in order for it to actually move upand down to follow the ground, its dynamics will still be governed byits mass and higher ground forces will be required to actually lift theheader. An implication of this arrangement is that the lower the staticground force is set, the slower the header is able to fall. This isbecause the maximum input force into the float system to make the headerfall is equal to the floated weight of the header. Therefore, thesmaller the floated weight of the header, the smaller the resultingacceleration. The existence of friction within the system will alsofactor into how light the float system is able to be. Friction createsan asymmetry between the required ground force when lifting and loweringthe header. This leads to higher ground force when lifting and slowermovement when lowering. This also creates a limit to how light thestatic ground force can be set as the floated weight must be larger thanthe friction in the system in order for the header to actually be ableto fall after being lifted.

The float system of the present invention allows these limitations to bereduced because the force applied by the float system can be controlledbased on the header's state of motion. Based on the sensor feedbackcollected, the controller can actually add more force to the system whenthe header is being lifted in order to help it lift more quickly withless ground force. Additionally, when the header starts to fall, thecontroller can decrease the applied force so that it falls more quickly.By being able to adjust the force provided by the float system based onthe header's state of motion, the dynamics of the header can be alteredso that it is no longer governed solely by the mass of the header. Thiscan allow a heavy header to not only have acceptable ground force whenstationary, but also lift and lower as though it actually has less mass.This also circumvents the limitation that the minimum downwardsacceleration is tied to the floated weight of the header, allowing thefloat system's stationary ground force to also be lower than could beachieved with a conventional float system.

It is desirable to provide mechanical improvements such as reducedsystem friction, a smaller dead band in the hydraulic valve and reducinghydraulic restriction for flow traveling into and out of the cylindersince these will reduce the amount of intervention required by thecontroller to produce favourable dynamics. Improving the quality of thefeedback signals to reduce the effects of noise (both mechanical andelectrical) provides the controller with more reliable data from whichto make control decisions.

The intention of a float system is to reduce the ground force of aheader in order to reduce wear and improve ground followingcapabilities. To date, all float systems are based on a static balanceof the implement. In other words, a force is applied such that it liftsa portion of the header's weight so that the ground force is lower.Provided the header is not moving up or down throughout its float range,this system is effective at reducing ground force. For example, if aheader weighs 7000 lbs and the float system is set to carry 6800 lbs,then only 200 lbs needs to be reacted by the ground. However,considering only the static state of the system neglects two importantfactors; friction and inertia.

In a friction-less system, the ground force is the same whether theheader is being lifted or lowered (assuming this is done very slowly).However, when friction is introduced in the system, the ground force isno longer the same when lifting and lowering. In fact, the differencebetween the ground force when lifting and lowering is equal to twice thefriction in the system. As a result of friction, there is a minimumground force which can be achieved. If this minimum threshold isexceeded, the header will no longer fall under its own influence afterit is lifted as the floated weight of the header is not sufficient toovercome friction. While minimizing the friction in the system can helpto reduce this effect, it will still represent a limitation of thesystem.

Another important short-coming of basing a float system on the staticbalance of the header is that the dynamics of the header will still begoverned by the header's weight when it is in motion. Based on Newton'ssecond law:

$a_{header} = {\frac{F_{float} + F_{ground}}{m_{header}} - g}$

Thus a 7000 lbs header (with no friction), set to 200 lbs static groundforce can only achieve a maximum downwards acceleration of 0.03 g. Italso requires 900 lbs of ground force to accelerate the header upwardsat 0.1 g. While the static ground force can be set reasonably light, thelighter this becomes, the slower the header is capable of falling afterbeing lifted. Also, the slope of the line (and consequently the groundforce required to produce a given acceleration) remains tied to the massof the header, not to the set point of the float system. As a result ofthis limitation, the header will still respond dynamically like it is7000 lbs; all the float system is able to change is the static groundforce of the system. When the effect of friction is combined with thislimitation, it is unsurprising that there are limitations to how lightan existing float system can get before its ground followingcapabilities are compromised.

In order to try and improve the dynamic response of the float system,the float system needs to not only change the static ground force, butalso how much ground force is required to lift and lower the header. Thehydraulic float system described herein achieves this is by introducingfeedback regarding the dynamic state of the system into the floatcontrol system. While a wide number of different measurements can beused to infer information regarding the dynamic state of the system(such as force, hydraulic pressure or other kinetic measurements), asdescribed herein, the extension of the float cylinder is measured with apotentiometer and this signal can be differentiated numerically todetermine the full kinematic state of the system.

In order to alter the dynamics of the header using the float system, theinput force from the float system cannot remain constant, but insteadmust vary with respect to the dynamic state (velocity and acceleration)of the header. The goal of the control algorithm is to not only reducethe static ground force when the header is stationary, but also toreduce the amount of force required to lift the header and to allow theheader to fall more quickly (as though it were a lighter header). Such asystem allows for lower ground force as well as better ground followingcapabilities. A dynamically changing force applied by the float systemcan reduce the impact of friction within the system.

The target pressure calculated by the position, velocity andacceleration state of the cylinder is generated by using a simple PIDcontroller. This PID intermittently looks at the difference between thetarget pressure and the measured pressure and then adjusts the output totry and minimize the error. The PID controller can be supplemented withan open-loop lookup table. The ability to robustly and reliably maintainthe cylinder pressure at the target pressure facilitates the developmentof a responsive and stable cylinder response.

Dithering is superimposed on the output to the PWM valve in attempt toreduce the amount of hysteresis in the system. Dithering is theintentional addition of “noise” into the signal. In this setup,sinusoidal dithering waves were used. It should be noted that while theoutput of the controller can be sinusoidal, the achieved pressurefluctuation is not necessarily perfectly sinusoidal due to the abilityof the hydraulics to replicate the input signal. This dithering signalwas calculated and simply added to the output of the PID controller toobtain the total output to the valve.

There are three parameters which can be controlled to change the natureof the dithering; the wave's amplitude, period and shape (sinusoidal,square, triangular, etc.). A variety of different parameters can be usedto try and reduce hysteresis and improve the response of the system.

Relatively effective dithering can be achieved with a dithering waveperiod of only 80-100 msec and an amplitude of only no of the overalloperable PWM duty cycle range although both a longer period and higheramplitude dithering wave can be necessary to achieve a similar result.

The period of the dithering wave appears to be bounded on the low end bythe responsiveness of the PRR valve as well as the ability to deliverthe flow required to move the cylinder. Above this lower limit, theeffect of the dithering wave is more directly related to the power inputof each half waveform. Consequently, a higher amplitude waveform isnecessary at shorter dithering periods, while a lower amplitude waveformcan be used with a longer dithering wave period. By maintaining adithering magnitude of 7% and varying the dithering period at shortdithering periods of <150 msec were not particularly effective.Dithering periods of 200-250 msec are effective, whereas if thedithering period is increased further, the header can noticeably shake.This shaking could be reduced by lowering the amplitude of the waveformso that the power of each half waveform is lower. However, it is best tokeep the dithering period as low as possible in order to help improvethe reaction time of the system, so the shortest dithering period whichis effective should be selected.

Any required motion will only be aided by half of the dithering waveformand hindered by the other half of it. It is helpful to interpret thedithering wave as the controller consecutively checking to see if theheader wants to lift, and then checking if it wants to lower. The amountof power in the dithering half-wave required to perform these checkswill relate to both the friction in the system as well as theresponsiveness of the hydraulics. It is helpful to disable ditheringwhen in a lifting or lowering state as half of the dithering wave willbe acting against the intended motion.

Pressure, position, velocity and acceleration inputs into the controlstructure are calculated as follows. As discussed previously, thecylinder is kept in constant motion by having the pressure in thecylinder always varying slightly by having a sinusoidal wave applied tothe valve output (referred to as dithering). This can make it moredifficult to determine the pressure and position of the cylinder as thisadds a substantial amount of noise. As a result, filtering and averagingtechniques are used to try and distinguish the bulk movement of thesystem while ignoring the motion caused by dithering. These techniquescan retain more responsiveness by using the properties of the ditheringwave instead of simply filtering more aggressively.

Since dithering creates variation in both the pressure in the cylinderas well as the position, both of these values are averaged over a singledithering wave period in order to try and reduce the influence thatdithering has on their calculation. A shorter dithering period istherefore desirable to help improve responsiveness of this calculation.

Since the velocity and acceleration terms are based on a differencecalculation, these are performed differently than the position andpressure terms; instead of looking at only a single dithering period,these calculations look at the last two dithering periods. The position(or velocity) is then compared at equivalent locations within thedithering wave. This allows for the calculation to be sensitive tochanges in position which are lower in magnitude than those created bythe dithering wave. Again, the calculation is averaged over a singledithering period. The velocity is calculated by looking at how much theposition has changed between comparable locations in the ditheringwaveform. In order for a hydraulic float system to produce adequateground following capabilities, it is desirable for it to mimic theresponse of a spring. In order to simulate a spring-like effect, theextension of the cylinder is used to vary the cylinder pressure. In thissetup, a simple linear spring rate was added. The spring rate isintroduced by creating a linear function which determines the targetpressure based on the measured cylinder extension. This made therequired input force get higher as the wing was lifted higher. The belowequation shows the most recent spring rate used to alter the header'sdynamics:

$P_{target} = {{P\lbrack{psi}\rbrack} - \left( {{0.26\left\lbrack \frac{psi}{mm} \right\rbrack}*{y\lbrack{mm}\rbrack}} \right)}$

Based on the current spring-based system, it is believed that having theheader get heavier as it gets lifted is beneficial. This has the effectof biasing the header so that it naturally wants to fall. However,provided that the target pressure at a given height leads to a non-zeroground force, the header should always want to fall. If terrain leads toextended periods of time spent with the header either raised or lowered,these periods of time occur with ground force which is either lighter orheavier than the set point. Provided the spring rate is not setparticularly aggressively, this is likely not an issue, however, theremay be value to having a more even header response throughout its rangeof motion to avoid it either being too light and wanting to lift offwhen too heavy and inclined to push when too light.

In one arrangement, the header's set point pressure can follow around amoving average of the header's position. This is an effective way toimplement a spring rate without sacrificing header pressure performancewhen spending extended periods of time away from its normal position.Such an arrangement makes the header initially want to return to itslast position (by either getting heavier when lifted or lighter whenlowered), but have it adapt to a change in position if it is maintainedfor a period of time.

In addition to having the dynamics of the header change with respect tothe header's position through the use of a spring rate, the header'spotentiometer signal is also used to change the target pressure withrespect to velocity and acceleration. As described previously, both thevelocity and acceleration terms were calculated in a way as to try andminimize the detection of movement caused by dithering so as to onlyfocus on the header's bulk movement

The velocity term relates to the damping of the system. However, sincethe header already had an over-damped response, this term is used to tryand reduce the damping of the system by reinforcing the motion of theheader. This term has some similarities to lift and lower assistpressures except instead of adding a constant pressure to the target,the effect varies with the magnitude of the header's velocity. It shouldbe noted that this term would have the effect of tending to de-stabilizethe header. It is helpful to create a nonlinear velocity-based functionwhich restricts smaller velocities and reinforces larger velocities. Itwould also likely be beneficial to make this term saturate at a maximumvalue to ensure this effect does not reduce the require ground force tolift the header below zero (which would cause the header to continue toaccelerate upwards until it reached full raise.

$P_{target} = {{P\lbrack{psi}\rbrack} + \left( {{6.0\left\lbrack \frac{psi}{{mm}/s} \right\rbrack}*{\overset{.}{y}\left\lbrack \frac{mm}{s} \right\rbrack}} \right)}$

The acceleration term relates to the inertia of the system. Byreinforcing accelerations, the controller is able to reduce theeffective inertia of the header to help it to react to input forces asthough it weighed less. However, in practice, taking a numerical secondderivative of a sensor input is inherently noisy, so the ability toimplement this is limited. That said, there is still value toincorporating a term which ties target pressure directly to theacceleration of the header to some extent. While initially a singleconstant is used, this term can be split into two parameters; one tocontrol the impact of positive accelerations and one to control theimpact of negative accelerations.

$P_{target} = {{{P\lbrack{psi}\rbrack} - {\left( {{0.4\left\lbrack \frac{psi}{{mm}/s^{2}} \right\rbrack}*{\overset{¨}{y}\left\lbrack \frac{mm}{s^{2}} \right\rbrack}} \right)\mspace{14mu}{for}\mspace{14mu}\overset{¨}{y}}} \geq 0}$$P_{target} = {{{P\lbrack{psi}\rbrack} + {\left( {{0.06\left\lbrack \frac{psi}{{mm}/s^{2}} \right\rbrack}*{\overset{¨}{y}\left\lbrack \frac{mm}{s^{2}} \right\rbrack}} \right)\mspace{14mu}{for}\mspace{14mu}\overset{¨}{y}}} < 0}$

Positive accelerations relate to when ground force is increased and theheader starts to lift, or when the header impacts the ground afterfalling. In order to help the header stick after it lands on the ground,positive accelerations were used to decrease the target pressure of thecontroller somewhat. This makes the header heavier momentarily when itcontacts the ground to help stop it from bouncing up again. This doesalso have the effect of make the header somewhat heavier when you firsttry to lift it. However, since the acceleration of the header impactingthe ground is notably larger than the acceleration input when liftingthe header, the effect is more noticeable in the case of an impact.

Negative accelerations relate to when the header slows down whilelifting and begins to fall. In order to help stop the header fromhanging up, negative accelerations are also used to decrease the targetpressure of the header, making it momentarily heavier and therefore lesslikely to hang up. If you begin to slow down the rate at which you liftthe header, it starts to get heavier.

It is possible to develop nonlinear equations which use the position,velocity and acceleration states of motion (as well as other variablessuch as ground speed, cut height, etc.) to extensively customize thedynamic response of the system.

Translating the control structure's target pressure into the outputfloat force of the system quickly, and accurately is important foroptimizing the system response. While the closed loop PID structure isquite effective at replicating the target pressure, more advancedcontrol techniques can help to further improve this response. Theinclusion of an open loop lookup table and downgrading the PIDcontroller to a correction factor can be used. It is possible to reducethe impact of valve lag by providing momentary overshoots in the currentoutput to the solenoid to help it change directions more quickly.

Reliably and robustly measuring the position, velocity and accelerationof the cylinder is required for responsively controlling the floatdynamics without introducing instability. It is desirable that thesecalculations provide a clean signal with as little lag as possible. Inthe current configuration, all calculations are tied to the ditheringperiod, regardless of whether dithering is actually active. It may bebeneficial to move towards two distinct calculations; one when ditheringis active and one when it is not. This may help to allow for higherresponsiveness is situations where noise caused by dithering does notneed to be accounted for.

The hydraulic float system described herein provides a float systemwhich is more responsive, with improved ground following capabilitiesand a lower ground force. The system is based on using an electroniccontroller and feedback from sensors in order to decide what pressureshould be supplied to the hydraulic float cylinder. This pressure isthen supplied by using a proportional pressure reducing/relieving valvebased on the output signal from the controller. The resultant systemallows for a highly customizable hydraulic pressure (and consequentlyforce) provided by the float system. This allows for the float system toadjust the force provided by the float system in order to reduce theeffects of friction in the system as well as to fundamentally alter thedynamics of how the header moves.

As shown therefore in FIG. 6, there is provided a crop harvestingmachine comprising a self-propelled support vehicle 102 for running overground carrying a crop to be harvested.

The crop cutting header includes at least one ground engaging componentsuch as cutter bar 89 for providing a supporting force from the groundas it runs over the ground. A support apparatus including the links 96,the spring 95 and the cylinder 94 provides a variable spring liftingforce for supporting the header from the vehicle for upward and downwardfloating movement of the header.

A control system 88 is arranged to provide a value of the lifting forceapplied by the spring to the header so that a predetermined proportionof a supporting force on the header is supplied by the spring and aremaining portion is supplied by the cutter bar 89 in engagement withthe ground.

The control system includes a control algorithm which operates inresponse to a ground speed signal from a sensor 87 to temporarily changethe lifting force.

The crop cutting header is of the type which comprises a rotary mowerhaving a plurality of transversely spaced cutting disks 91 on the cutterbar 90 as is conventionally known. However other headers can be usedwith this same system.

The control system 88 is arranged by the algorithm in the software suchthat the lifting force provided by the spring 95 is reduced by thecylinder 94 to reduce the lifting force provided by the spring and thusto increase the weight of the header on the ground when the ground speedis higher.

The lifting force provided by the spring is reduced to increase theweight of the header on the ground when the ground speed is greater than5 mph as indicated by the sensor 87. The lifting force is reduced toincrease the weight of the header on the ground proportional to groundspeed as controlled by the algorithm of the control system 88 inresponse to the signal from the sensor 88. The algorithm is arrangedafter the temporary increase generated by the increase in ground speedto reduce the lifting force to revert back to a set value suitable forthe lower speed of around 5 mph. Alternatively as the speed reduces asdetected by the sensor 88, the lifting forces is reduced by a valuedirectly or indirectly proportional to the ground speed.

Also the control system is arranged to temporarily vary the liftingforce in response to detected movement of the header relative to thevehicle as provided by the sensors previously described herein andindicated schematically in FIG. 6 at 86. As described previously thecontrol system can arranged to temporarily vary the lifting force inresponse to detected acceleration of the header relative to the vehicleand upon detection of an end of said acceleration to again vary thelifting force.

That is there is provided a position sensor 86 for generating a positionsignal indicative of a position of the header in the movement and thecontrol system is arranged to calculate from the position signal avelocity and acceleration of the header.

As described previously the algorithm of the control system can bearranged to provide a plurality of preset flotation weights fordifferent ground speeds.

The invention claimed is:
 1. A crop harvesting machine comprising: aself-propelled support vehicle for running over ground carrying a cropto be harvested; a crop cutting header including at least one groundengaging component for providing a supporting force from the ground asthe header runs over the ground; a support apparatus providing a liftingforce for supporting the header from the vehicle for upward and downwardfloating movement of the header; a control system configured to providea value of the lifting force so that a predetermined proportion of asupporting force is supplied by the support apparatus and a remainingportion is supplied by the at least one ground engaging component inengagement with the ground; a ground speed sensor for providing a groundspeed signal to the control system indicative of a ground speed of theheader; the control system being configured to 1) temporarily vary thelifting force in response to detected acceleration of the headerrelative to the vehicle, 2) decrease the lifting force upon detection ofan end of the acceleration in an upward floating movement of the header,and 3) temporarily change the value of the lifting force in response tothe ground speed signal.
 2. The crop harvesting machine according toclaim 1 wherein the crop cutting header comprises a rotary mower havinga plurality of transversely spaced cutting disks.
 3. The crop harvestingmachine according to claim 1 wherein the control system is arranged suchthat the lifting force is reduced to increase a weight of the header onthe ground when the ground speed is increased.
 4. The crop harvestingmachine according to claim 1 wherein the control system is arranged suchthat the lifting force is reduced to increase a weight of the header onthe ground when the ground speed is greater than 5 mph.
 5. The cropharvesting machine according to claim 1 wherein the control system isarranged such that the value of the lifting force is reduced to increasea weight of the header on the ground where the value is proportional toground speed.
 6. The crop harvesting machine according to claim 1wherein the control system is arranged such that the value of thelifting force is reduced to increase a weight of the header on theground in response to an algorithm dependent on the ground speed.
 7. Thecrop harvesting machine according to claim 1 wherein the control systemis configured to, after reducing the value of the lifting force, torevert to a set value.
 8. The crop harvesting machine according to claim1 wherein the control system is configured to temporarily vary the valueof the lifting force in response to detected movement of the headerrelative to the vehicle.
 9. The crop harvesting machine according toclaim 1 wherein the control system is configured to temporarily vary thevalue of the lifting force in response to detected acceleration of theheader relative to the vehicle.
 10. The crop harvesting machineaccording to claim 9 wherein the control system is configured to, upondetection of an end of said detected acceleration, to vary the value ofthe lifting force.
 11. The crop harvesting machine according to claim 1wherein there is provided a position sensor for generating a positionsignal indicative of a position of the header during the upward ordownward floating movement and wherein the control system is configuredto calculate from the position signal a velocity and/or acceleration ofthe header.
 12. The crop harvesting machine according to claim 1 whereinthe control system is configured to provide a plurality of preset valuesof lifting force each associated with a respective one of a plurality ofdifferent ground speeds.
 13. The crop harvesting machine according toclaim 1 wherein the support apparatus comprises a mechanical spring andwherein the control system is configured to vary a spring force of themechanical spring.
 14. A rotary mower comprising: a self-propelledsupport vehicle for running over ground carrying a crop to be harvested;a crop cutting header having a plurality of transversely spaced cuttingdisks and at least one ground engaging component for providing asupporting force from the ground as the header runs over the ground; asupport apparatus providing a lifting force for supporting the headerfrom the vehicle for upward and downward floating movement of theheader; a control system configured to provide a value of the liftingforce so that a predetermined proportion of a supporting force issupplied by the support apparatus and a remaining portion is supplied bythe at least one ground engaging component in engagement with theground; a sensor providing ground speed signals indicative of differentground speeds of the vehicle; the control system being configured to 1)temporarily vary the lifting force in response to detected accelerationof the header relative to the vehicle, 2) decrease the lifting forceupon detection of an end of the acceleration in an upward floatingmovement of the header, and 3) control the value of the lifting forcesuch that the lifting force has a first value at a first ground speedand a second value at a second ground speed higher than the first groundspeed where the second value of the lifting force at the second higherground speed is less than the first value of the lifting force at thefirst ground speed.
 15. The crop harvesting machine according to claim14 wherein the control system is configured such that the lifting forceis reduced to the second value when the ground speed exceeds apredetermined value.
 16. The crop harvesting machine according to claim14 wherein the control system is configured such that the value of thelifting force is inversely proportional to the ground speed.
 17. Thecrop harvesting machine according to claim 14 wherein the control systemis configured such that the value of the lifting force is related to theground speed by an algorithm dependent on ground speed.
 18. The cropharvesting machine according claim 14 wherein the control system isconfigured to, after reducing the value of the lifting force, to revertto a set value.
 19. The crop harvesting machine according to claim 14wherein the control system is configured to provide a plurality ofpreset values of lifting force each associated with a respective one ofa plurality of different ground speeds.